This application claims the priority of German application 196 47 964.9-14 filed in Germany on Nov. 20, 1996, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a process and apparatus for manufacturing slot-shaped openings on hollow sections with the openings being generated without cut outs by the displacement of material using a piercing cutting operation by means of a blade type cutting tool while supporting the hollow sections from the interior during slotting operation.
A process and apparatus of this type are known from German Patent Document DE 43 34 203 A1. There, passages are made in a linearly extending collecting pipe of a heat exchanger, in which case several punches, which are arranged in parallel to one another and are fastened on a carrier part and have blades constructed on their free ends, are jointly moved radially onto the hollow section to be worked which forms the collecting pipe. In this case, the punches tear the passages into the wall of the hollow section at the point of application. A rod-shaped tool with support sections is pushed into the hollow section, which support sections, in the appropriate position of the tool, are positioned between the application points of the hollow section for maintaining the shape of the hollow section. With the pushing-through of the hollow section by the punches, the hollow section material is displaced at that point, in which case the edge of the passage to be produced is bent while forming a wall neck projecting into the hollow section. The contact of the wall neck on the support sections ensures a rectangular course of the wall neck so that the hollow section has a defined seat for the flat tubes, which are fitted into the passages, for a later tight soldering. As a result of the bending of the penetration edges and their resting on the support sections of the rod-shaped tool, this tool is blocked with respect to an axial pulling out of the hollow section so that the tool cannot easily be removed from the hollow section to be worked. This is remedied by a bipartition of the tool, in which case first a lower half of the tool can be removed by a simple pushing-out; after which the upper half is rotated until it comes to rest below the bent edges. Then this half can also be pulled out.
In another embodiment, the tool, which now consists of one part, only partially fills the cross-section of the hollow section so that a clearance is formed which extends axially along the whole length of the hollow section. In this case, after the machining of the hollow section, the support tool is lowered and is pulled out of the hollow section.
In the case of both embodiments, the tool has a high-expenditure construction because of the support sections, in which case, they must have an extremely precisely adjusted distance from one another so that the hollow section can meet the precision requirements for the assembly with the flat tubes. At the same time, the handling of the tool requires high expenditures since it must be positioned in a precisely defined manner relative to the cutting tool. Because of the unavoidable positioning tolerances, the danger exists during the machining on the hollow section that one of the oblong punches will bend because it strikes a point of the hollow section wall which is supported by the support tool or is situated in the edge area of the respective support section, whereby the cutting tool may possibly be irreparably damaged. Likewise, the hollow section may also be damaged such that disadvantageous incisions occur on it which, particularly when the hollow section is used as a liquid-carrying component having sealing problems, will result in an increased reject rate of hollow sections. Furthermore, in the one case, the two-part support tool must be held together during the pushing-in and must be rotated when being removed after the machining, which results in lost production time. In the other case, for an effective support, a high holding force must be applied which is directed against the penetration force of the cutting tool, so that it is avoided that the one-part support tool is pressed into the clearance inside the hollow section under the effect of the cutting tool and, in the process, the support is impaired which is required for maintaining the shape of the hollow section.
The thickness of the bent edge at the points of the hollow section acted upon by the punches and the width of the respective support section of the rod-shaped support tool also determine the distance between the passages or openings. However, as a result, very small hollow sections may be too limited in their dimensions in order to be provided with several passages or openings by means of the described device.
In addition, the described manufacturing process and the device for its implementation can be used only in the case of linear hollow sections. Other shapes of hollow sections with cross-sectional changes and/or changes of course, such as bent pipes, cannot be provided with openings in this manner.
It is an object of the invention to further develop a process and apparatus of the above-mentioned type such that, in a simple manner and while maintaining the shape of the hollow section, slot-shaped openings can be manufactured in a reliable process on arbitrarily constructed hollow sections free of positional tolerances.
According to the invention, this object is achieved by a process and apparatus wherein, as a result of interaction between cutting action of the cutting tool integrated in an internal high pressure forming tool and an internal high pressure of a fluid generated within a hollow section disposed in a recess of the internal high pressure forming tool, the hollow section is slotted in a relative movement of the hollow section and of the cutting tool with respect to one another, with continuous, interior-side support of the hollow section by means of the pressure fluid, the support at the point of the piercing of the cutting tool into the hollow section being pushed back and the hollow section material, which is flowable under internal high pressure, flowing off laterally from respective piercing points around the piercing points while forming a wall thickening on the hollow section, and wherein the outer contour of the hollow section being pressed by means of internal high pressure against a contour of a face of a cutting tool carrier which is separate with respect to the cutting tool but is integrated with the cutting tool, which face forms a portion of the forming tool recess which faces the hollow section.
Because of the arrangement of the invention, a support tool can be eliminated because the support takes place by the internal high pressure applied inside the hollow section which loads the wall on all sides. In this case, only an internal-high-pressure forming tool is required into whose recess the hollow section is placed, in which case the die of the forming tool has a recess in which the cutting tool together with the support is accommodated. If the hollow section is also calibrated for exact dimensions which are uniform for all hollow sections to be machined, an internal-high-pressure forming tool is required anyhow so that in this case no additional tool--with the exception of the cutting tool--must be used. The recess may be constructed corresponding to the shape of the hollow section with respect to cross-sectional changes and to the axial course so that the device and the process are not subjected to any limitations in this respect. Furthermore, the construction of the slot-type openings takes place in a completely reliable manner with respect to the process because the cutting tool is never in any danger of impacting on a hard support object on which it may be damaged. Because of the recess of the forming tool which is adapted precisely to the hollow section and because of the non-existent requirement of positioning a support tool to be pushed into the hollow section, as well as the integration of the cutting tool into the forming tool in which the cutting tool takes up a defined relative position with respect to the forming tool, the hollow section, the cutting tool and the forming tool, which results in the support within the hollow section, are always positioned precisely with respect to one another in the machining position, in which case no manufacturing tolerances can occur. By means of the simultaneous support of the outer circumference of the hollow section on the recess, no deformations of the original shape of the hollow section will occur so that, as the result, the dimensional accuracy of the hollow section as a whole is maintained. The forming of the hollow section and the providing of the openings on it take place in the same tool and therefore in one operating cycle without the requirement of opening the tool and setting it up again for the cutting operation.
Furthermore, by means of the invention, very small-construction hollow sections can also be provided with a large number of openings because a support section of a discussed tool of a finite width and the thickness of the hollow section wall which determines the width of the immersion gap for the blade of the cutting tool, are eliminated. The minimum distance between the openings is therefore determined only by the blade width of the cutting tool, advantageously, also in the case of larger-construction hollow sections, several openings being formable on a partial section. Virtually because of the existing internal pressure, the hollow section material displaced by the blade flows laterally away from the blade and is pressed against the hollow section wall surrounding the respective opening, which, in the case of the finished hollow section, is exhibited in a wall thickening. Because of the displacement of material, the cutting of the hollow section takes place without any occurrence of cuttings and without waste.
Finally, openings can be achieved which have sharp-edged margins and thus no bending radii on the exterior side of the section. This maximizes the support surface for add-on pieces to be mounted later so that, during the mounting, the Hertzian stress is distributed as well as possible.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.